How to get rid of cockroaches

Work out which cockroach you have first

In New Zealand this genuinely changes what you should do. Large native and Gisborne cockroaches wander in from outside and don't establish indoors - those you can simply put back out and proof against. German cockroaches are small, tan, and breed indoors fast; those need treating properly.

Seeing one during the day is the signal that matters. Cockroaches are nocturnal, so daytime activity usually means the harbourage is crowded.

Find the harbourage, not the cockroach

Cockroaches spend most of their time hidden somewhere warm, dark and close to food and moisture. Treating the surfaces you see them on achieves very little because they aren't there most of the time.

• Behind and underneath the fridge, especially the warm motor housing
• Under and behind the dishwasher and oven
• Inside cupboard voids, particularly under the sink
• Around and inside floor drains
• Behind kickboards and in the gaps at the back of built-in units

What actually works

Gel bait placed at the harbourage points, not sprayed around. Bait gets carried back and shared through the population; contact spray kills what it hits and pushes the rest somewhere new.

Alongside that, remove what they're living on: food debris under appliances, pet bowls left out overnight, standing water, cardboard packaging stored in warm cupboards.

Why they come back a week later

Cockroach eggs sit in a hard case that most treatments don't penetrate, so a batch hatches a week or two after the first knock-down. That's normal and expected - it's why a serious infestation is planned as more than one treatment rather than a single spray.

If you've treated it yourself and it's back within a fortnight, that's the egg hatch rather than a failed product.

When to stop and call someone

If you're seeing them in daylight, finding egg cases, or it's a food business, DIY is unlikely to hold. The same applies in a flat or apartment - populations move between units through shared walls and service risers, so treating one unit while the neighbours don't means it walks straight back.